1. Field of the Invention
The present invention relates in general to the field of transmission line analysis.
2. Description of Related Art
The following abbreviations are herewith defined, at least some of which are referred to in the ensuing description of the prior art and the preferred embodiment of the present invention.    CO Central Office    CPM Copper Plant Management System    DSL Digital Subscriber Line    ETSI European Telecommunications Standards Institute    ETSIxx Cable Reference Model According to ETSI/STC TM6(97)02, Revision 3: 970p02r3, e.g., ETSI50 depicts 0.50 mm cable.    NB-SELT Narrow Band Single-Ended Line Test    POTS Plain Old Telephone Service    SELT Single-Ended Line Test
An operator of a telecommunication network has a great interest in measuring the properties of their transmission lines. Because, they can use the results of such measurements for e.g. detecting faults, locating faults, predicting certain faults which are about to occur, and estimating the suitability and capacity of a transmission line for certain services, such as DSL. The operator can use a variety of tests to measure the properties of a transmission line. For example, the operator can use a POTS test so they can maintain and diagnose a customer's narrowband (4 kHz) connection.
In addition, the operator can perform a single-ended line test (e.g., NB-SELT) in which properties of a transmission line can be estimated from measurements made at one end of the line. For instance, the single-ended line test enables the length of the transmission line to be measured by sending a pulse and measuring the time until a reflected pulse is received back. In addition, the single-ended line test enables the capacitance of the transmission line to be estimated by applying a voltage to the transmission line, then removing it and measuring the voltage decay time. Unfortunately, there is not a single-ended line test available today which can be used to detect the presence of a load coil in a transmission line. The ability to detect a load coil is desirable. Because, if there is a load coil present within the transmission line then that would disqualify the transmission line from supporting a DSL service. But, if the operator can detect a load coil then they could remove the load coil so the transmission line can now support a DSL service. This is made possible by the present invention.